Ehrlichia in Florida

Florida Situation. An unusual cluster of 4 ehrlichiosis cases in Jefferson county in August 2001 prompted the county health office to declare a medical alert. One case was fatal. One case was confirmed as E. chaffeensis; the others are considered probable E. chaffeensis.

Typically, there are 1-2 cases of ehrlichiosis reported in the state each year. Thus, a cluster of 4 cases in one county is a dramatic increase above "normal". We do not know what conditions led to this increase, but it is likely to be related to tick populations and tick-human contact.

Human ehrlichioses. Ehrlichia are bacteria, related to Rickettsia, and are obligate intracellular parasites. Several species of Ehrlichia cause disease in humans and domestic animals. These bacteria have only recently begun to receive much research attention, and there are still many questions about their transmission cycles and reservoir hosts. There are likely to be taxonomic revisions of Ehrlichia and Anaplasma as further research occurs.

Ehrlichiosis is differentiated based on the mammalian cell type infected. Monocytes, granulocytes and neutrophils are most frequently involved, and the common name of the resulting disease reflects the cell type (monocytic or granulocytic ehrlichiosis). The two major types of human ehrlichiosis in the eastern U.S. are human monocytic ehrlichiosis (HME), caused by E. chaffeensis; and human granulocytic ehrlichiosis (HGE), caused by E. phagocytophila.

Clinically, the different types of ehrlichiosis are difficult to differentiate. Symptoms include fever, headache, malaise and muscle aches. Rashes occur more frequently with HME than HGE. Treatment for both types are antibiotics in the tetracycline family, most commonly doxycycline. Fatalities are rare with either, but can occur as the result of complications from infection. Complete diagnosis requires serological or molecular tests to differentiate Ehrlichia species, but treatment should begin after clinical diagnosis. Asymptomatic infections probably occur with all Ehrlichia. Improved diagnostic tools and an increased awareness of ehrlichiosis are revealing that these infections are more common than previously suspected.

  Ehrlichia chaffeensis - HME Ehrlichia phagocytophila - HGE
Vectors Amblyomma americanum (lone star tick); possibly Dermacentor variabilis (American dog tick) In the eastern US, Ixodes scapularis (black-legged tick or deer tick). Elsewhere, other members of the I. ricinus group (I. ricinus, I. pacificus)
Distribution HME has been diagnosed from every state in the U.S. except the Dakotas. More common in the southeastern U. S., largely congruent with the distribution of A. americanum U. S., Europe. In the U. S., this species has been reported from areas where I. scapularis and I. pacificus are present, predominately in the northeast, midwest and California. Cases have been identified in Florida, but the level of transmission is unclear.
Reservoir Hosts probably deer, rodents and/or dogs probably rodents, possibly deer
Disease humans, rarely dogs humans, horses, dogs, cattle

Prevention and Management. As with any vector-borne disease, the primary preventive measure is to minimize contact with the tick vectors. Protective clothing, such as long pants and socks tucked into pants will reduce tick contact. Repellents containing DEET are effective against most ticks. Permethrin-based repellents can be sprayed on boots and clothing. Thorough tick checks and prompt removal of attached ticks will reduce transmission of tick-borne disease. Use fine-tipped forceps to remove ticks; grasp the tick near the skin and pull straight back. Do not squeeze the abdomen or apply heat or petroleum products; this may cause the tick to regurgitate into the host!

Tick population reduction is difficult and it is unclear how effective it will be in reducing infection rates. Various methods have been tested, including vegetation management, acaracide treatment, host exclusion and host treatment. Treatment of hosts, via treated feed or feeding stations that apply acaricide to hosts, are promising methods for population reduction of ticks which feed on deer.

Further information:

Cynthia C. Lord, Ph.D.
Florida Medical Entomology Lab